Semiconductor multilevel interconnect structure

ABSTRACT

A method of fabricating a semiconductor multilevel interconnect structure employs a dual hardmask technique in a dual damascene process. The method includes using amorphous carbon as a first hardmask layer capable of being etched by a second etch process, and a second hardmask layer capable of being etched by a first etch process, as a dual hardmask. By virtue of the selective etch chemistry employed with the dual hardmask, the method affords flexibility unattainable with conventional processes. The via is never in contact with the photoresist, thus eliminating residual photoresist at the trench/via edge and the potential “poisoning” of the intermetal dielectric layer. Since trench/via imaging is completed before further etching, any patterning misalignments can be easily reworked. Because the amorphous carbon layer and the second hardmask layer are used as the dual hardmask, the photoresist can be made thinner and thus optimized for the best imaging performance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of semiconductor memoryand logic devices. The invention relates more specifically to a methodof fabricating a semiconductor multilevel interconnect structure, aswell as the resulting structure.

2. Description of the Related Art

In order to improve the speed of semiconductor devices on integratedcircuits, it has become desirable to use conductive materials, such ascopper, having low resistivity and low k (a dielectric constant of lessthan 4.0) in order to reduce the capacitive coupling between structuressuch as interconnect lines.

Because materials such as copper are difficult to etch in a precisepattern, a method of fabrication known as a dual damascene process canbe used to form the interconnects. In a conventional dual damasceneprocess, a dielectric layer is etched to define both the contacts andvias, and the interconnect lines. Metal is then inlaid into the definedpattern and any excess metal is removed from the top of the structure ina planarization process, such as chemical mechanical polishing.

In order to provide the interconnects such as those fabricated fromcopper, various approaches have been proposed. For example,photolithography using an SiO₂/SiN_(x) dual hardmask for an organic lowk dual damascene process is known. In another approach, described inU.S. Pat. No. 6,291,334, a low k etch stop material, such as anamorphous carbon, is deposited between two dielectric layers and is thenpatterned to define the underlying interlevel contacts/vias. The entiredual damascene structure is then etched in a single selective etchprocess which first etches the patterned interconnects, then etches thecontact/vias past the patterned etch stop. The etch stop has a lowdielectric constant relative to a conventional SiN etch stop, therebyminimizing the capacitive coupling between adjacent interconnect lines.

In still another approach, described in U.S. Pat. No. 6,297,554, a dualdamascene process is employed to produce a structure having at least onetrench in the surface of a dielectric layer, an insulating layer in thetrench, and at least one void in the insulating layer. The insulatinglayer can consist of a low dielectric constant material such asamorphous carbon. The void is used to reduce the effective dielectricconstant of the dielectric layer so as to reduce the parasiticcapacitance between two adjacent copper wiring lines.

Despite the benefits of using interconnects such as those fabricatedfrom copper, there can be certain drawbacks associated with use of aconventional dual damascene process. First, the conventional process canleave an undesirable “ear” (or “fence” or “fender”) formation ofphotoresist residue at the trench/via edge. FIG. 6 is a partialcross-sectional view of a structure 300 fabricated by a conventionaldual damascene process. Once the bulk of the photoresist has beenremoved, a residue of photoresist 340 may still be left on intermetaldielectric layer (IMD) 310 at each of the trench 330/via 320 edges. Thepresence of the photoresist residue can adversely affect the performanceof the multilevel interconnect.

Secondly, one of the major problems associated with dual damasceneintegration, especially when a low k IMD layer is used, is the“poisoning” of the IMD which can result from the interaction between thephotoresist and the IMD. The poisoning, which occurs during applicationof the photoresist, arises because a low k IMD material, which isrelatively porous, can absorb chemicals associated with the photoresist.The subsequent outgassing of these chemicals during via metallizationleads to structural defects in the via. Neither of the above-describedconventional dual damascene processes overcomes either of thesedrawbacks.

Thirdly, another drawback associated with conventional dual damasceneprocesses is their lack of flexibility. For example, with theconventional process, the IMD may be partially etched before the trenchand/or via patterning are completed. If there is any misalignment in thetrench/via patterning, it cannot be corrected once the IMD has beenetched.

Finally, in conventional dual damascene processes, the photoresist isoptimized not for imaging performance, but rather, for its etchresistance. That is, because the photoresist must be etch resistant(i.e., relatively thick) in a conventional process, the imagingqualities of the photoresist may be compromised for the benefit of etchperformance.

Therefore, a need exists for a method of dual damascene fabricationwhich not only avoids the formation of residual photoresist and avoidspoisoning of the IMD, but which provides flexibility in patterning andprovides for optimization of the photoresist for imaging performance.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method of fabricating a semiconductormultilevel interconnect structure, as well as the resulting structure.More specifically, the present invention provides a dual damascenemethod of fabrication using a dual hardmask technique that mitigates theabove-described deficiencies associated with conventional processes.

Accordingly, the present invention relates to a dual damascene, dualhardmask, method of fabrication using amorphous carbon as a firsthardmask layer capable of being etched by a second etch process, and asecond hardmask layer capable of being etched by a first etch process.By virtue of the selective etch chemistry employed with the dualhardmask, the present method affords flexibility unattainable withconventional dual damascene processes.

The method includes forming a via and trench associated with theinterconnect structure by selectively etching a layer of amorphouscarbon as a first hardmask layer capable of being etched by a secondetch process, and etching a second hardmask layer capable of beingetched by a first etch process. The method also includes usingprotective layers to isolate intermetal dielectric layers from layers ofphotoresist applied during the fabrication process.

The present invention is also directed to a structure for use infabricating a dual damascene opening according to the above-describedmethod of fabrication. The structure includes a first layer comprising afirst intermetal dielectric layer and a metal portion; a firstprotective layer on the first layer; a second intermetal dielectriclayer on the first protective layer; a second protective layer on thesecond intermetal dielectric layer; a layer of amorphous carbon as afirst hardmask layer on the second protective layer; a second hardmasklayer on the amorphous carbon layer; and a patterned layer ofphotoresist on the second hardmask layer.

The present method and structure have several advantages overconventional dual damascene processes and structures. First, by virtueof the protective layers, the via, after being opened, is never incontact with the photoresist. This eliminates the “ear” formationproblem at the trench/via edge which results from the presence ofphotoresist residue on the IMD layer.

Secondly, this processing sequence eliminates the potential “poisoning”of the IMD layer which can result from the interaction between thephotoresist and the IMD layer during application of the photoresist.

Thirdly, the photolithographic imaging for both the trench and the viaare completed before the IMD etch, so, if necessary, it is easy torework any patterning misalignments to ensure that both the trench andthe via are etched correctly.

Fourthly, the conventional dual damascene requirement that thephotoresist be etch resistant is not a constraint with the presentmethod. That is, because the amorphous carbon layer and the secondhardmask layer are used as the dual hardmask, the photoresist can bemade thinner and thus optimized for the best imaging performance.Finally, because each of the hardmask layers is ultimately removed inthe fabrication sequence, they do not impact the final IMD structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome more fully apparent from the following detailed description ofthe exemplary embodiments of the invention which are provided inconnection with the accompanying drawings.

FIG. 1 is a partial cross-sectional view of a structure constructed inaccordance with the present invention for use with a multilevelinterconnect.

FIGS. 2A-J illustrate a first embodiment of the method of fabricatingthe structure depicted in FIG. 1.

FIGS. 3A-C are a flow diagram of the fabrication sequence correspondingto FIGS. 2A-J.

FIGS. 4A-I illustrate a second embodiment of the method of fabricatingthe structure depicted in FIG. 1.

FIGS. 5A-C are a flow diagram of the fabrication sequence correspondingto FIGS. 4A-I.

FIG. 6 is a partial cross-sectional view of a structure fabricated by aconventional method that leaves photoresist residue on the intermetaldielectric layer at the trench/via edge.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a partial cross-sectional view of an interconnect structure100 constructed in accordance with the present invention for use with amultilevel interconnect. Structure 100, the fabrication of which isdescribed below, includes a first layer 110 having a first intermetaldielectric layer 111 and a metal portion 112; an etched protective layer120; an etched second intermetal dielectric layer 130; a via 170; and atrench 190. Structure 100 can accommodate the deposition of an inlaidmultilevel interconnect metal. As is evident from FIG. 1, structure 100is characterized by the absence of any undesirable “ear” (i.e.,structural formation of resist residue) on the etched IMD layer 130 atthe trench/via edge.

FIGS. 2A-J illustrate a first embodiment of the method of fabricatingthe structure 100 depicted in FIG. 1. FIGS. 3A-C are a flow diagram ofthe fabrication sequence corresponding to FIGS. 2A-J. The methodincludes first assembling a dual hardmask structure to be etched. Asdepicted in FIG. 2A, a first layer 110 comprising a first intermetaldielectric layer 111 and a metal portion 112 is formed (step 1010). Themetal of metal portion 112 may be Cu or any other metal typicallyemployed as a multilevel interconnect. A first protective layer 120 isdeposited (step 1020) upon the first layer 110. The first protectivelayer 120 typically comprises a material selected from the groupconsisting of silicon nitrides, silicon carbo-nitrides, and siliconcarbides.

A second intermetal dielectric layer 130 is deposited (step 1030) uponthe first protective layer 120. A second protective layer 135 isdeposited (step 1035) upon the second intermetal dielectric layer 130.The second protective layer 135 typically comprises a material selectedfrom the group consisting of silicon oxides, silicon nitrides, siliconcarbo-nitrides, silicon carbides, and titanium nitrides. In anotherembodiment, the second protective layer 135 can be a dielectricantireflective coating. The second protective layer 135 serves toprotect the underlying second intermetal dielectric layer 130 frompossible contamination associated with exposure to thesubsequently-deposited photoresist (described below).

A layer of amorphous carbon as a first hardmask layer 140 capable ofbeing etched by a second etch process (described below) is deposited(step 1040) upon the second protective layer 135. A second hardmasklayer 150 capable of being etched by a first etch process (describedbelow) is deposited (step 1050) upon the amorphous carbon layer 140.Then, in the final step of assembling the layered structure prior toetching, a first layer of photoresist 160 is deposited (step 1060) uponthe second hardmask layer 150 and patterned with an opening 161 throughwhich etching will occur.

The amorphous carbon layer 140, which can be deposited as a PECVD film,has a very slow etch rate for the etch chemistry associated with thematerial of the second hardmask layer 150 (i.e., the etch selectivitycan be as high as 100:1). Furthermore, amorphous carbon can be easilyetched with an etch chemistry (described below) that does not etch thesecond hardmask layer 150. This unique property of amorphous carbonmakes it possible to use, for example, a stack of the amorphous carbonlayer 140 and the second hardmask layer 150 as a dual hardmask in thepresent dual damascene process.

The second hardmask layer 150 typically comprises a material selectedfrom the group consisting of silicon oxides, silicon nitrides, siliconcarbo-nitrides, silicon carbides, and titanium nitrides. In anotherembodiment, the layer of material 150 can be a dielectric antireflectivecoating.

Next, in the first etching step, a first portion of a via 170 is formedby etching (FIG. 2B)(step 1070) the second hardmask layer 150 using afirst etch process. The first etch process, which etches the secondhardmask layer 150, typically employs a plasma containingC_(x)F_(y)H_(z). An oxide, for example, can be easily etched by a plasmahaving C_(x)F_(y)H_(z) (e.g., CF₄), but is not etched at all by any ofthe etchants (described below) that may be used to etch the amorphouscarbon layer 140.

In the next via-patterning step, a second portion of the via 170 isformed by etching (FIG. 2C)(step 1080) the amorphous carbon layer 140using a second etch process. During step 1080, for the following tworeasons, the first layer of photoresist 160 is completely consumed.First, the photoresist layer 160 is etched by the same etchant as is theamorphous carbon layer 140. The photoresist layer 160 etches faster thanamorphous carbon layer 140 because the amorphous carbon is harder thanphotoresist. Secondly, because a dual hardmask is employed, and becausea second layer of photoresist 180 (FIG. 2D) is employed for subsequentetching steps (described below), the photoresist layer 160 can be arelatively thin layer, having a thickness chosen to provide the optimalphoto-imaging performance. The photoresist layer 160 typically has athickness of from 1000 to 6000 Å.

The second etch process, which etches the amorphous carbon layer 140,typically employs an etchant selected from the group consisting of O₂plasma, N₂ and O₂ plasma, N₂O plasma, NO plasma, H₂ plasma, and NH₃plasma. For example, with O₂ plasma, or a plasma of N₂ and O₂, the layerof material 140 can be easily etched and results in the release of CO₂.With H₂ plasma or NH₃ plasma, the amorphous carbon layer 140 can beeasily etched and results in the release of CH₄.

Next, before trench patterning is begun, a second layer of photoresist180 is deposited (FIG. 2D)(step 1090) on the etched second hardmasklayer 150 and patterned with an opening 181 through which etching willoccur. A first portion of a trench 190 is then formed by etching (FIG.2E)(step 1100) the etched second hardmask layer 150 through opening 181using the first etch process. The amorphous carbon layer 140 is anexcellent etch stop because amorphous carbon layer 140 is notselectively etched with the etched second hardmask layer 150.

In addition, because of the presence of second protective layer 135, thesecond intermetal dielectric layer 130 is advantageously never exposedto the photoresist 180, thus avoiding any potential poisoning of thelayer 130. This feature of the present invention, therefore, minimizesthe potential for poisoning that can arise with conventional processesin which the via is fully opened to the level of the intermetaldielectric layer before the second layer of photoresist is applied,thereby exposing the intermetal dielectric layer to direct contact withthe photoresist.

A third portion of the via 170 is then formed by etching (FIG. 2F)(step1110) the second protective layer 135 and the second intermetaldielectric layer 130 using the first etch process. In this step, theetched amorphous carbon layer 140 is used as a hardmask to effect thevia etch through the second protective layer 135 and the secondintermetal dielectric layer 130, and some of the photoresist 180 isconsumed. The via etch can be a full via etch stop on the protectivelayer 120 as shown in FIG. 2F, or a partial etch. The second protectivelayer 135 and the second intermetal dielectric layer 130 are etched withthe first etch process, typically by a plasma containing C_(x)F_(y)H_(z)(e.g., CF₄).

A second portion of the trench 190 is formed by etching (FIG. 2G)(step1120) the etched amorphous carbon layer 140 using the second etchprocess. In this step, the etched second hardmask layer 150 serves asthe hardmask, and trench patterning is effected through the etchedamorphous carbon layer 140 as the photoresist 180 is completelyconsumed.

In the next step, trench etching of the etched second protective layer135 and the etched second intermetal dielectric layer 130 is effectedusing the first etch process, with the etched amorphous carbon layer 140serving as the hardmask. Thus, a third portion of the trench 190 isformed by etching (FIG. 2H)(step 1130) the etched second protectivelayer 135 and the etched second intermetal dielectric layer 130 andthereby removing all of the etched second hardmask layer 150.

The etched amorphous carbon layer 140 is then removed by etching (FIG.2I)(step 1140) using the second etch process without in any way damagingthe etched second intermetal dielectric layer 130. This step of etchingto remove the amorphous carbon layer 140 typically employs theabove-described etchant selected from the group consisting of O₂ plasma,N₂ and O₂ plasma, N₂O plasma, NO plasma, H₂ plasma, and NH₃ plasma.Alternatively, the etching to remove the amorphous carbon layer 140 mayemploy a hot non-plasma etchant selected from the group consisting ofO₂, O₃, N₂O, NO, H₂, and NH₃. Without plasma, however, the etch isisotropic, and the gaseous etchant must be employed at an elevatedtemperature. Other non-plasma etchants may be employed to remove theamorphous carbon layer 140, such as compounds of the formulaC_(x)F_(y)H_(z), but with these etchants the etch rate is much slowerthan that attainable with either the above-described plasma etchants(i.e., O₂ plasma, N₂ and O₂ plasma, N₂O plasma, NO plasma, H₂ plasma,and NH₃ plasma) or hot non-plasma etchants (i.e., O₂O₃, N₂O, NO, H₂, andNH₃).

The etched second protective layer 135 and a portion of the firstprotective layer 120 that is disposed above the metal portion 112 arethen removed by etching (FIG. 2J)(step 1150) using the first etchprocess so as to complete the formation of the via 170. The resultantstructure 100 is thus ready for deposition of the inlaid interconnectmetal.

The etch chemistry of the photoresist layers 160 and 180 is similar tothe etch chemistry of the amorphous carbon layer 140, but thephotoresist etches faster because amorphous carbon is harder thanphotoresist. As indicated above, in conventional dual damasceneprocesses, the photoresist is optimized not for imaging performance, butrather, for its etch resistance. That is, because the photoresist mustbe etch resistant (i.e., relatively thick) in a conventional process,the imaging qualities of the photoresist may be compromised for thebenefit of etch performance. An advantage of the present invention isthat because the amorphous carbon layer 140 and the second hardmasklayer 150 are used as the dual hardmask, the photoresist can be madethinner and thus optimized for the best imaging performance.

FIGS. 4A-I illustrate a second embodiment of the method of fabricatingthe structure 100 depicted in FIG. 1. FIGS. 5A-C are a flow diagram ofthe fabrication sequence corresponding to FIGS. 4A-I. As with the firstmethod embodiment, the method includes first assembling a dual hardmaskstructure to be etched. In this second embodiment of the method, thefirst five steps of assembling the layered structure (steps 2010, 2020,2030, 2040, and 2050) are identical to the first five steps describedabove (steps 1010, 1020, 1030, 1040, and 1050) for the first embodimentof the method of fabrication.

As depicted in FIG. 4A, a first layer 210 comprising a first intermetaldielectric layer 211 and a metal portion 212 is formed (step 2010). Themetal of metal portion 212 may be Cu or any other metal typicallyemployed as a multilevel interconnect. A first protective layer 220 isdeposited (step 2020) upon the first layer 210. The first protectivelayer 220 typically comprises a material selected from the groupconsisting of silicon nitrides, silicon carbo-nitrides, and siliconcarbides.

A second intermetal dielectric layer 230 is deposited (step 2030) uponthe first protective layer 220. A second protective layer 235 isdeposited (step 2035) upon the second intermetal dielectric layer 230.The second protective layer 235 typically comprises a material selectedfrom the group consisting of silicon oxides, silicon nitrides, siliconcarbo-nitrides, silicon carbides, and titanium nitrides. In anotherembodiment, the second protective layer 235 can be a dielectricantireflective coating. The second protective layer 235 serves toprotect the underlying second intermetal dielectric layer 230 frompossible contamination associated with exposure to thesubsequently-deposited photoresist (described below).

A layer of amorphous carbon as a first hardmask layer 240 capable ofbeing etched by a second etch process (described below) is deposited(step 2040) upon the second protective layer 230. A second hardmasklayer 250 capable of being etched by a first etch process (describedbelow) is deposited (step 2050) upon the amorphous carbon layer 240.Then, in the final step of assembling the layered structure prior toetching, a first layer of photoresist 260 is deposited (step 2060) uponthe second hardmask layer 250 and patterned with an opening 261 throughwhich etching will occur. Because a dual hardmask is employed, andbecause a second layer of photoresist 280 is employed for subsequentetching steps (described below), the photoresist layer 260 can be arelatively thin layer, having a thickness chosen to provide the optimalphoto-imaging performance. The photoresist layer 260 typically has athickness of from 1000 to 6000 Å.

The amorphous carbon layer 240, which can be deposited as a PECVD film,has a very slow etch rate for the etch chemistry associated with thematerial of the second hardmask layer 250 (i.e., the etch selectivitycan be as high as 100:1). Furthermore, amorphous carbon can be easilyetched with an etch chemistry that does not etch the second hardmasklayer 250. This unique property of amorphous carbon makes it possible touse, for example, a stack of the amorphous carbon layer 240 and thesecond hardmask layer 250 as a dual hardmask in the present dualdamascene process.

The second hardmask layer 250 typically comprises a material selectedfrom the group consisting of silicon oxides, silicon nitrides, siliconcarbo-nitrides, silicon carbides, and titanium nitrides. In anotherembodiment, the layer of material 250 can be a dielectric antireflectivecoating.

Next, in the first etching step, a first portion of a trench 270 isformed by etching (FIG. 4B)(step 2070) the second hardmask layer 250using a first etch process. The amorphous carbon layer 240 is anexcellent etch stop because amorphous carbon layer 240 is notselectively etched with the second hardmask layer 250.

The first etch process, which etches the second hardmask layer 250,typically employs a plasma containing C_(x)F_(y)H_(z). An oxide, forexample, can be easily etched by a plasma containing C_(x)F_(y)H_(z)(e.g., CF₄), but is not etched at all by any of the etchants (describedbelow) that may be used to etch the amorphous carbon layer 240.

A second layer of photoresist 280 is then deposited (FIG. 4C)(step 2080)upon the etched second hardmask layer 250 and on a portion of theamorphous carbon layer 240 and patterned with an opening 281 throughwhich etching will occur. A first portion of a via 290 is formed byetching (FIG. 4D)(step 2090) the amorphous carbon layer 240 using asecond etch process. Because of the presence of second protective layer235, the second intermetal dielectric layer 230 is advantageously neverexposed to the photoresist 280, thus avoiding any potential poisoningreaction with the layer 230.

The second etch process, which etches the amorphous carbon layer 240,typically employs an etchant selected from the group consisting of O₂plasma, N₂ and O₂ plasma, H₂ plasma, and NH₃ plasma. For example, withO₂ plasma, or a plasma of N₂ and O₂ the layer of material 240 can beeasily etched and results in the release of CO₂. With H₂ plasma or NH₃plasma, the amorphous carbon layer 240 can be easily etched and resultsin the release of CH₄.

A second portion of the via 290 is then formed by etching (FIG. 4E)(step2100) the second protective layer 235 and the second intermetaldielectric layer 230 using the first etch process. A second portion ofthe trench 270 is formed by etching (FIG. 4F)(step 2110) the etchedamorphous carbon layer 240 using the second etch process. In this step,the second layer of photoresist 280 is removed, and the etched secondhardmask layer 250 serves as the hardmask.

A third portion of the trench 270 is formed by etching (FIG. 4G)(step2120) the etched second protective layer 235 and the etched secondintermetal dielectric layer 230 using the first etch process and therebyremoving all of the etched second hardmask layer 250. In this step, theetched amorphous carbon layer 240 serves as the hardmask.

The etched amorphous carbon layer 240 is then removed by etching (FIG.4H)(step 2130) using the second etch process. This step of etching toremove the amorphous carbon layer 240 typically employs theabove-described etchant selected from the group consisting of O₂ plasma,N₂ and O₂ plasma, N₂O plasma, NO plasma, H₂ plasma, and NH₃ plasma.Alternatively, the etching to remove the amorphous carbon layer 240 mayemploy a hot non-plasma etchant selected from the group consisting ofO₂, O₃, N₂O, NO, H₂, and NH₃. Without plasma, however, the etch isisotropic, and the gaseous etchant must be employed at an elevatedtemperature. Other non-plasma etchants may be employed to remove theamorphous carbon layer 240, such as compounds of the formulaC_(x)F_(y)H_(z), but with these etchants the etch rate is much slowerthan that attainable with either the above-described plasma etchants(i.e., O₂ plasma, N₂ and O₂ plasma, N₂O plasma, NO plasma, H₂ plasma,and NH₃ plasma) or hot non-plasma etchants (i.e., O₂, O₃, N₂O, NO, H₂,and NH₃).

The etched second protective layer 235 and a portion of the firstprotective layer 220 that is disposed above the metal portion 212 arethen removed by etching (FIG. 41)(step 2140) using the first etchprocess so as to complete the formation of the via 290. The resultantstructure 100 is thus ready for deposition of the inlaid interconnectmetal.

The etch chemistry of the photoresist layers 260 and 280 is similar tothat of the etch chemistry of the amorphous carbon layer 240, but thephotoresist etches faster because amorphous carbon is harder thanphotoresist. As indicated above, in conventional dual damasceneprocesses, the photoresist is optimized not for imaging performance, butrather, for its etch resistance. That is, because the photoresist mustbe etch resistant (i.e., relatively thick) in a conventional process,the imaging qualities of the photoresist may be compromised for thebenefit of etch performance. An advantage of the present invention isthat because the amorphous carbon layer 240 and the second hardmasklayer 250 are used as the dual hardmask, the photoresist can be madethinner and thus optimized for the best imaging performance.

The present invention is also directed to a structure 101 depicted inFIG. 2A (201 depicted in FIG. 4A) for use in fabricating a dualdamascene opening according to the above-described first and secondembodiments of the method of fabrication. As depicted in FIG. 2A (FIG.4A), structure 101 (201) comprises a first layer 110 (210) comprising afirst intermetal dielectric layer 111 (211) and a metal portion 112(212). A first protective layer 120 (220) is disposed on the first layer110 (210), and a second intermetal dielectric layer 130 (230) isdisposed on the first protective layer 120 (220). A second protectivelayer 135 (235) is disposed on the second intermetal dielectric layer130 (230). A layer of amorphous carbon as a first hardmask layer 140(240) capable of being etched by a second etch process is disposed onthe second protective layer 135 (235), and a second hardmask layer 150(250) capable of being etched by a first etch process is disposed on theamorphous carbon layer 140 (240). A layer of photoresist 160 (260) isdisposed on the second hardmask layer 150 (250) and has an opening 161(261) through which etching will occur.

The present invention, therefore, provides a method and structure havingseveral advantages over conventional dual damascene processes andstructures. By virtue of the features described herein, such as theselective etch chemistry employed with the dual hardmask, the presentmethod affords flexibility unattainable with conventional dual damasceneprocesses. First, by virtue of the protective layers, the via, afterbeing opened, is never in contact with the photoresist. This eliminatesthe “ear” formation problem at the trench/via edge which results fromthe presence of photoresist residue on the IMD layer.

Secondly, this processing sequence eliminates the potential “poisoning”of the IMD layer which can result from the interaction between thephotoresist and the IMD layer during application of the photoresist.

Thirdly, the photolithographic imaging for both the trench and the viaare completed before the IMD etch, so, if necessary, it is easy torework any patterning misalignments to ensure that both the trench andthe via are etched correctly.

Fourthly, the conventional requirement that the photoresist be etchresistant is not a constraint with the present method. That is, becausethe amorphous carbon layer and the second hardmask layer are used as thedual hardmask, the photoresist can be made thinner and thus optimizedfor the best imaging performance. Finally, because each of the hardmasklayers is ultimately removed in the fabrication sequence, they do notimpact the final IMD structure.

Although the invention has been described and illustrated as beingsuitable for use in semiconductor fabrication applications, theinvention is not limited to these embodiments. Rather, the inventioncould be employed in any service in which the flexibility and benefitsassociated with the above-described features would be desirable.

Accordingly, the above description and accompanying drawings are onlyillustrative of exemplary embodiments that can achieve the features andadvantages of the present invention. It is not intended that theinvention be limited to the embodiments shown and described in detailherein. The invention is limited only by the scope of the followingclaims.

1-42. (canceled)
 43. A structure for use in fabricating a dual damasceneopening, said structure comprising: a first layer comprising a metalportion; a first protective layer on said first layer; an intermetaldielectric layer on said first protective layer; a second protectivelayer on said second intermetal dielectric layer; an amorphous carbonlayer as a first hardmask layer on said second protective layer; and asecond hardmask layer on said amorphous carbon layer.
 44. A structureaccording to claim 43, wherein said first protective layer comprises amaterial selected from the group consisting of silicon nitrides, siliconcarbo-nitrides, and silicon carbides.
 45. A structure according to claim43, wherein said second protective layer comprises a material selectedfrom the group consisting of silicon nitrides, silicon carbides, andsilicon carbo-nitrides.
 46. A structure according to claim 43, whereinsaid second hardmask layer comprises a material selected from the groupconsisting of silicon oxides, silicon nitrides, silicon carbo-nitrides,silicon carbides, and titanium nitrides.
 47. A structure according toclaim 43, wherein said second protective layer is a dielectricantireflective coating.
 48. A structure according to claim 43, whereinsaid second hardmask layer is a dielectric antireflective coating.
 49. Astructure according to claim 43, wherein said metal portion is Cu.
 50. Astructure for use in fabricating a dual damascene opening, saidstructure comprising: an amorphous carbon layer as a first hardmasklayer; a second hardmask layer on said amorphous carbon layer; and aphotoresist layer on said second hardmask layer, said photoresist layerhaving a thickness of from 1000 to 6000 Å.